Sagittarius stars
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Sagittarius Stars: A Comprehensive Overview
Discovery of New Stars in Sagittarius
New Star Detection in Sagittarius
In the late 19th century, a new star was discovered in the constellation Sagittarius by Mrs. Fleming during the examination of the Draper Memorial photographs. The exact date of its appearance is uncertain but is estimated to be either in late 1897 or early 1898 .
Massive Stars in the Sagittarius Dwarf Irregular Galaxy
Low Metallicity Massive Stars
The Sagittarius Dwarf Irregular Galaxy (SagDIG) is notable for hosting low metallicity massive stars, which are crucial for understanding various cosmic processes such as re-ionization and high-redshift supernovae. Recent observations have identified three OBA-type stars and one red supergiant candidate in SagDIG, potentially making them the most metal-poor massive stars in the Local Group .
Star Formation History
An optical monitoring survey of SagDIG revealed continuous star formation activity over its lifetime, with varying rates. The study identified 27 long-period variable stars, including asymptotic giant branch stars and red supergiants, which helped estimate the star formation rate and total stellar mass within SagDIG .
Chemical Abundance and Kinematics of Sagittarius Stream Stars
Chemical Abundance Signatures
The APOGEE survey has provided detailed chemical abundances for red giant stars in the Milky Way, including those in the Sagittarius dwarf spheroidal galaxy (Sgr). The chemical patterns of Sgr stars are distinct from those of the Milky Way, allowing for the identification of stars that have been stripped from Sgr during its interactions with the Milky Way .
Radial Velocities and Metallicity
High-resolution spectroscopy of stars in the Sagittarius streams has shown that stream stars are generally more metal-poor than those in the main body of Sgr. This difference is more pronounced in stars from older wraps of the stream, supporting models of Sgr's disruption .
Diffuse Metal-poor Component
The H3 Stellar Spectroscopic Survey has revealed a diffuse, metal-poor component of the Sagittarius stream. This component, which spans a wide range of metallicities, is thought to have been stripped from the Sagittarius progenitor at earlier epochs and resides at larger radii compared to the colder, metal-rich component .
Structure and Kinematics of the Sagittarius Spiral Arm
Parallax Measurements
The BeSSeL Survey has measured parallaxes and proper motions of high-mass star-forming regions in the Sagittarius spiral arm. These measurements have helped determine the structure and kinematics of the arm, including its pitch angle and distance from the Sun .
New OB Stars
The SDSS-IV/APOGEE2 survey has identified a large sample of new O- and B-type stars along the Sagittarius spiral arm. This discovery includes 95 mid- to late-O-type stars and 38 early- to mid-B-type stars, significantly expanding the known population of massive stars in this region .
Stellar Populations in the Sagittarius Dwarf Spheroidal Galaxy
Age and Metallicity
The Sagittarius dwarf spheroidal galaxy hosts a nuclear star cluster (NSC), M54, which contains three distinct stellar populations: young metal-rich, intermediate-age metal-rich, and old metal-poor. These populations exhibit different age-metallicity relations and kinematic properties, suggesting varied formation histories Johnson2020Boer2015.
Kinematic Characterization
Detailed kinematic studies of M54's stellar populations have shown that the old metal-poor population has low rotation and follows a Plummer profile, while the young metal-rich population exhibits high rotation and flattening. These differences indicate distinct formation paths, with the old population likely resulting from globular cluster accretion and the young population forming in situ from gas accretion .
Conclusion
The constellation Sagittarius and its associated dwarf galaxies and streams offer a rich field for studying star formation, chemical abundances, and kinematics. From the discovery of new stars to the detailed analysis of stellar populations, ongoing research continues to unravel the complex history and structure of this fascinating region of the sky.
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